The present invention relates generally to a method and a system for measuring the content of particles dispersed in a solvent and, more specifically, to a method and a system for monitoring the toner content in ink contained in a recording head for a printer.
There are electrostatic ink-jet printers in which high-speed high-quality printing is achieved by discharging a jet of charged toner contained in liquid ink by means of electric field.
In such an ink-jet printer, just after discharging a jet of charged toner, a jet of toner has to be quickly prepared for the next discharge for a higher speed, and the toner content in a jet of toner (to be more precise, a jet of toner is a mixture of charged toner and ink) has to be more than a certain level for a higher printing quality without any blot or blur. Thus, in order for this kind of ink-jet printer to exhibit its advantages such as a high speed and a high printing quality, the toner content in ink has to be kept at a sufficient level.
There have been proposed techniques for detecting the presence of electrified toner by means of actinometry or resistance measurement and for warning the user to supply toner. However, since the measurements are performed only in a binary fashion, such toner detecting techniques can not be used for maintaining a predetermined charged toner content in ink.
Japanese unexamined patent publication No. Hei2-102061 (1990) discloses a system for detecting the ink residual quantity. In this system, the level of the surface of ink is detected by knowing whether the optical path of the detecting system is above the surface level or not. For this reason, this system can not measure the charged toner content in ink.